S = SearchForest2( [[]],                           	 # root
	lambda l: [l+[0], l+[1]] if len(l) < 20 else [], # children
	lambda x: x,                                     # post-process
	lambda x: var('x')**len(x),                      # statistic
	lambda x,y: x+y,                                 # reduce_function
	0 )                                              # reduce_init
